diff --git a/main.py b/main.py
index 2e01839..7b9857f 100644
--- a/main.py
+++ b/main.py
@@ -1,5 +1,6 @@
 import datetime
 import logging
+import random
 import re
 import sys
 import time
@@ -169,7 +170,10 @@ def on_ready_for_otp(e: Event, commandor: CommandorPage):
 def start_book():
     start_slot_number = 1
     end_slot_number = 21
-    for i in range(start_slot_number, end_slot_number + 1):
+    slot_list = list(range(start_slot_number, end_slot_number + 1))
+    random.shuffle(slot_list)
+    for i in slot_list:
+        random.shuffle(params.MODEM_POOL_PORTS)
         card_pool.reset()
         logger.info("will switch to " + str(i))
         global current_card_pool_slot
diff --git a/wait_for_sms.py b/wait_for_sms.py
index a2f9af3..1acfd9c 100644
--- a/wait_for_sms.py
+++ b/wait_for_sms.py
@@ -1,4 +1,5 @@
 import logging
+import random
 import sys
 import time
 from typing import Union
@@ -86,7 +87,10 @@ def start_waiting_sms():
     params.oracle_log_sender.send_wait_sms_log()
     slot_number = 1
     slot_sum = 21
-    for i in range(slot_number, slot_sum + 1):
+    slot_list = list(range(slot_number, slot_sum + 1))
+    random.shuffle(slot_list)
+    for i in slot_list:
+        random.shuffle(params.MODEM_POOL_PORTS)
         card_pool.reset()
         logger.info("will switch to " + str(i))
         card_pool.switch_to_slot(i)